1. Field of the Invention
The present invention relates to a sheet processing system including a sheet processing device having a space portion as a sheet discharge unit, a sheet post-processing device removably attached into the space portion, and a sheet reversing path.
2. Description of the Related Art
A sheet post-processing such as punching, binding, and sorting performed on an image-formed sheet of paper is increasingly required of recent image forming systems. However, a sheet post-processing device that performs the sheet post-processing thereon is connected to an outer side surface of an image forming apparatus of a type that discharges the sheet from the side surface of the body of the apparatus. This configuration causes an installation space of the image forming system to be increased.
On the other hand, there are image forming apparatuses of a type that has a space portion within the installation area (inside the body of the apparatus) of the image forming apparatus and discharges a sheet of paper into the space portion, and some of the image forming apparatuses have various types of sheet post-processing devices attached into the space portion, as disclosed in Japanese Patent Application Laid-open No. 2006-206271, Japanese Patent Application Laid-open No. 2004-155566, and Japanese Patent No. 3898358.
Provided in the image forming apparatus is a plurality of sheet feeding units in order to form an image on one side or on both sides of the sheet. A switching unit is also provided therein to appropriately switch one sheet feeding unit to another for use according to a process mode.
One of the conventional image forming apparatuses is explained below. This image forming apparatus has a configuration in which various types of sheet post-processing devices can be attached into the space portion and images can be formed on both sides of the sheet.
FIG. 11 is a front view of an external configuration of the conventional image forming apparatus. The image forming apparatus is composed of a sheet feeding unit A, an image forming unit B, and an image reading unit C. Provided below the image reading unit C is a space portion D in which sheets of paper image-processed by the image forming unit B are discharged and stored. A sheet discharge unit D1 is provided in a lower part of the space portion D, and the sheets are sequentially discharged and stacked on the sheet discharge unit D1.
FIG. 12 is a schematic for explaining an internal configuration and an operation of a sheet conveying path in the image forming apparatus in FIG. 11. The sheet conveying path includes conveying roller pairs 1 and 2 being a feeding unit that forms a first sheet conveying path along which a sheet S of paper stacked in the sheet feeding unit A is fed; conveying roller pairs 5, 7, 8, and 9 that form a second sheet conveying path for reversing the sheet; an image transfer portion 3 of the image forming unit B that forms an image on the sheet; a sheet-discharge roller pair 4 that discharges the sheet onto the sheet discharge unit D1 in the space portion D; a reversing roller pair 6 that is made to rotate forwardly and reversely so as to reverse the sheet when an image is formed on both sides of the sheet; and a switching claws t1 to t3 that are switching units for switching one sheet conveying path to another for use and provided at respective guiding branches.
Operations when an image is formed on one side of the sheet in the image forming apparatus in FIG. 12 are explained below with reference to FIGS. 13A and 13B.
First, the image forming unit B acquires image information from an external device or from the image reading unit C, and processes the image information. Then, as shown in FIG. 13A, the sheet S is conveyed from the sheet feeding unit A to the image transfer portion 3 in the image forming unit B by the conveying roller pairs 1 and 2 in the first sheet conveying path, and an image forming process is performed therein. Thereafter, as shown in FIG. 13B, a sheet S1 which is the sheet S with the image formed on its one side is guided by the switching claw t1 to a sheet discharge path, and the sheet S1 is discharged onto the sheet discharge unit D1 in the space portion D by the sheet-discharge roller pair 4 in the sheet discharge path.
Operations when images are formed on both sides of the sheet are explained below with reference to FIGS. 14A to 14E.
As shown in FIG. 14A, the sheet S is conveyed from the sheet feeding unit A to the image transfer portion 3 in the image forming unit B, where an image is formed on the sheet S, and the sheet S1 is sent to a vertical conveying path by the switching claw t1. As shown in FIG. 14B, the sheet S1 is conveyed to the reversing path by a conveying guide formed with the conveying roller pair 5 and the switching claw t2. As shown in FIG. 14C, the sheet S1 is continuously conveyed by the reversing roller pair 6. However, when the trailing edge of the sheet S1 passes through the switching claw t2, as shown in FIG. 14D, the switching claw t2 is switched and further the reversing roller pair 6 is reversed, and the sheet S1 is thereby switched back and starts to be conveyed to a right-side conveying path. Thereafter, the sheet S1 is conveyed to a vertical reversing path by the switching claw t3, and is continuously conveyed as it is by the conveying roller pairs 7, 8, and 9. The sheet S1 again passes through the conveying roller pair 2, and, as shown in FIG. 14E, an image is formed on the other side of the sheet S1 at the image transfer portion 3. Thereafter, the sheet S1 is fed to a sheet discharge path by the switching claw t1, and is discharged on the sheet discharge unit D1 in the space portion D by the sheet-discharge roller pair 4.
Next, operations when a sheet discharge tray E is attached to an outer upper portion of the image forming apparatus and the sheet is discharged onto the sheet discharge tray E are explained with reference to FIGS. 15A to 15C.
As shown in FIG. 15A, the sheet S is conveyed from the sheet feeding unit A to the image transfer portion 3 in the image forming unit B, where an image is formed on the sheet S. The sheet S1 is sent to the vertical conveying path by the switching claw t1, and is once conveyed to the reversing path by the conveying guide formed with the conveying roller pair 5 and the switching claw t2. The sheet S1 is continuously conveyed by the reversing roller pair 6. However, as shown in FIG. 15B, when the trailing edge of the sheet S1 passes through the switching claw t2, the switching claw t2 is switched and further the reversing roller pair 6 is reversed, and the sheet S1 is thereby switched back and starts to be conveyed to the right-side conveying path. Thereafter, as shown in FIG. 15C, the sheet S1 passes through the switching claw t3, and is sequentially stacked on the sheet discharge tray E with its imaged side down by a sheet discharge roller 10 provided in the sheet discharge tray E.
FIG. 16 is a schematic of the image forming apparatus when an additional sheet discharge unit U is attached thereinto. The additional sheet discharge unit U includes a sheet-discharge roller pair 13 and an additional sheet-stacking tray D2. The additional sheet-stacking tray D2 can be additionally provided in the space portion D of the image forming apparatus in the downstream side of the reversing roller pair 6 in the sheet conveying direction.
Thus, in both-side printing, when the sheet is to be reversed upon discharge of the sheet onto the sheet discharge tray E, the reversing roller pair 6 and the sheet-discharge roller pair 13 perform the same operation, and the sheet S is received on the additional sheet-stacking tray D2, so that the sheet can be reversed. Furthermore, by setting a sheet discharge destination to the additional sheet discharge unit U, the additional sheet-stacking tray D2 can be set and used as another sheet discharge destination which is different from the sheet discharge unit D1 being an ordinary sheet discharge destination.
In the conventional technologies, if the sheet post-processing device can be attached into the space portion (in-body space) in the image forming apparatus, an image forming system including the sheet post-processing device requires only an installation area equivalent to that for a single unit of the image forming apparatus. Thus, this system can achieve significant space saving as compared with an image forming system in which the sheet post-processing device is connected to the outside of the image forming apparatus.
As explained with reference to FIGS. 11 to 16, the image forming apparatus is in many cases provided with a sheet reversing path to form images on both sides of the sheet. In this case, after the image processing is performed on the both sides of the sheet or when the sheet is conveyed to the sheet post-processing device through the sheet reversing path, the conveying paths are too long if there is nothing to be done for the conveying paths. Thus, there is high possibility that some trouble may occur during sheet conveyance.